Cardiology

Background 

Asystole, also known as “flatline,” is a state of complete absence of ventricular electrical activity, resulting in no cardiac output and no pulse. It is a form of pulseless electrical activity (PEA) and represents one of the non-shockable rhythms in cardiac arrest. Without prompt identification and management, asystole is rapidly fatal. 

II) Classification/Types 

By Rhythm Status: 

• True asystole: Complete absence of electrical activity across the myocardium. 

• Pseudo-asystole: Apparent flatline due to technical issues (e.g., lead disconnection, artifact) or very fine ventricular fibrillation. 

By Underlying Mechanism: 

• Primary asystole: Resulting from intrinsic failure of the cardiac conduction system. 

• Secondary asystole: Due to severe metabolic, toxic, or ischemic insult suppressing myocardial activity. 

Pathophysiology 

Asystole results from the failure of impulse generation in the sinoatrial node and/or impulse conduction through the myocardium. It may follow a prolonged bradyarrhythmia or PEA. The myocardium becomes electrically and mechanically unresponsive, either due to extensive ischemia, severe electrolyte derangement, profound acidosis, or drug toxicity. 

Epidemiology 

• Common final event in in-hospital and out-of-hospital cardiac arrests 

• Represents up to 30–40% of non-traumatic adult cardiac arrests 

• Very poor prognosis compared to shockable rhythms (e.g., VF/pVT) 

Etiology 

I) Causes 

• Hypoxia 

• Hypovolemia 

• Hydrogen ion (acidosis) 

• Hyper-/hypokalemia 

• Hypothermia 

• Tension pneumothorax 

• Tamponade (cardiac) 

• Toxins (e.g., opioids, TCA, digoxin) 

• Thrombosis (pulmonary or coronary) 

• Trauma (severe hemorrhagic shock) 

II) Risk Factors 

• Advanced age 

• Structural heart disease (e.g., heart failure, MI history) 

• Chronic kidney disease (prone to hyperkalemia) 

• Drug overdose or polypharmacy 

• Recent cardiac surgery 

• Electrolyte imbalances or acid-base disturbances 

Clinical Presentation 

I) History (Symptoms) 

Often preceded by symptoms of bradycardia or cardiac instability: 

• Syncope or sudden collapse 

• Lightheadedness or dizziness 

• Chest discomfort 

• Dyspnea or palpitations 

• Seizure-like activity (due to cerebral hypoperfusion) 

II) Physical Exam (Signs) 

• No pulse 

• Unconscious, unresponsive 

• No heart sounds 

• Apnea 

• Cyanosis or pallor 

• Cardiac monitor showing flatline or near-flatline 

Differential Diagnosis (DDx) 

• Fine ventricular fibrillation 

• Severe bradycardia or PEA 

• Equipment malfunction or lead disconnection 

• Profound hypothermia 

• High-grade AV block without escape rhythm 

Diagnostic Tests 

Initial Work-Up 

• Cardiac monitor/ECG: Confirm true asystole (check leads and gain) 

• Pulse check: No palpable pulse 

• ABG/VBG: Assess for severe acidosis or hypoxia 

• Electrolytes and glucose: Identify correctable causes 

• Toxicology screen: If drug overdose suspected 

• Bedside ultrasound: Rule out tamponade or massive PE 

Advanced Testing 

(Not performed during arrest but post-resuscitation if ROSC achieved) 

• Cardiac biomarkers 

• CT chest or pulmonary angiogram (if PE suspected) 

• Echocardiogram for structural evaluation 

Treatment 

I) Acute Management (During Cardiac Arrest) 

Follow Advanced Cardiac Life Support (ACLS) for Asystole: 

• CPR: High-quality compressions at 100–120/min with minimal interruption 

• Epinephrine: 1 mg IV/IO every 3–5 minutes 

• Airway management: Bag-valve-mask ventilation or advanced airway 

• Identify and treat reversible causes (the H’s and T’s) 

• DO NOT DEFIBRILLATE: Asystole is non-shockable 

• Reassess rhythm every 2 minutes 

II) Post-Resuscitation (If ROSC achieved) 

• Manage underlying cause (e.g., correct hyperkalemia, initiate antibiotics for sepsis) 

• Hemodynamic support (vasopressors, fluids) 

• Targeted temperature management if comatose 

• Intensive care monitoring 

Medications 

Device Therapy 

• Temporary pacing: Rarely useful in true asystole unless known high-degree AV block with reversible etiology 

• Defibrillation: Not indicated in asystole 

• ECMO: Considered in select centers for refractory cardiac arrest (eCPR) 

Patient Education, Screening, Vaccines 

Education (Post-Recovery, if applicable) 

• Discuss resuscitation preferences and advance directives 

• Risk factor modification (e.g., medication review, K⁺ control) 

• Educate on warning signs of bradyarrhythmias 

Screening/Prevention 

• Monitor electrolyte and drug levels in high-risk patients 

• Regular ECG in patients with conduction disease or on nodal blockers 

• Avoid QT-prolonging or bradycardia-inducing drugs without indication 

Vaccinations 

• None specific to asystole 

• Routine adult immunizations encouraged (e.g., influenza, pneumococcus) 

Consults/Referrals 

• Cardiology: For post-resuscitation arrhythmia evaluation 

• Electrophysiology: For pacemaker consideration in advanced AV block 

• Critical Care: For post-arrest management 

• Nephrology: For electrolyte imbalance or dialysis needs 

• Toxicology: In suspected poisoning or overdose 

Follow-Up 

Short-Term 

• Monitor for organ dysfunction (e.g., AKI, anoxic brain injury) 

• Reevaluate need for pacing or ICD if conduction system disease suspected 

• Rehabilitation for post-cardiac arrest syndrome 

Long-Term 

• Ongoing cardiology follow-up 

• Neurological assessment and cognitive evaluation 

• Advance care planning discussions 

Prognosis 

• Extremely poor in true asystole without rapid ROSC 

• Worse outcomes compared to VF/pVT cardiac arrest 

• Prognosis improved with rapid CPR, early epinephrine, and reversible cause identification 

• Survivors often suffer from significant neurological impairment 

• If ROSC achieved and underlying cause treated, long-term survival is possible but uncommon